Q. The oil analysis on my 2006 Freightliner Century Class came back with a “caution” alert. Water in the oil was 0.18 percent. This seems a little high. How concerned should I be?

A. Water can get into engine oil a variety of ways. You could have a small leak at a gasket or seal. Or water can condense from the air. In the worst-case scenario, you could have cylinder-liner pitting that results in pinholes. Those allow coolant to leak from water jackets into the cylinder and then into the crankcase. If that were the case, you would have a cause for concern and would probably face a major overhaul. Thankfully, this is not the case with your engine.

The best way to tell if the water is from coolant is to check the amounts of sodium and potassium, according to Chuck Blake, my expert on Detroit Diesel Series 60 engines. Chuck is senior technical sales support manager at Detroit and has been representing his company at TMC for more than two decades.

The Silver Spark Plug awardee told Land Line that your analysis showed both elements were within normal range for a 2006 engine with more than 700,000 miles.

The critical level for water is 0.5 percent. A normal level is 0.05 percent, and 0.3 percent is marginal. Your 0.18 percent is worth monitoring, but it’s nothing to be concerned about now.

Keep an eye on your gauges. If the engine is running cool most of the time, Blake suggests you may need a new thermostat. Every time you change the thermostat or even open the housing to check it, make sure you change the gasket.

If you brought your truck in for service and it sat overnight, the water may have condensed from humidity in the crankcase. It’s always a good idea to drain oil as soon as practical after the oil is warm to avoid condensation. Also, warmer, thinner oil drains more completely.

It’s important to note that this question points up the importance of oil analysis as a preventive tool. It’s much easier to identify and correct a minor problem early than to wait until the problem becomes major. An engine teardown to discover where a problem might be is a very costly alternative. Oil analysis becomes a good investment by identifying potential problems early.

You can look at your results as an individual event or as a sequence. Each report will show whether the oil is still good to go or there are areas for concern.

For example, consider an alert limit for iron at 100 parts per million (ppm). If you have successive reports showing iron readings of 35, 38, 36 and 40 ppm, you have no concerns. But if the next report comes back at 76 ppm, even though well under the alert limit, you should be concerned. There is a dramatic change in the trend.

An individual report will not signal that there is cause for concern, but by plotting trends you will become aware of possible valve train or cylinder lining wear.

Keep your reports and, if possible, use a lab that will do this kind of dynamic analysis. You can learn more about interpreting results from TMC Recommended Practice RP318, Used Engine Oil Analysis.

Q. I have a 2008 Volvo VNL. Almost from the start, I’ve had slime in the fuel tank. Sometimes it clogs the filters. I never had this with my old truck. Is there something about this truck that causes it? What can I do about it?

A. There are several reasons, but none of them have to do with your truck. In 2006, fuel changed. Refiners met the ultra-low-sulfur diesel distribution deadline. Biodiesel production was increasing.

The sulfur had some beneficial properties, one of which is that it is a biocide, controlling organic growth.

Biodiesel has an affinity for water, absorbing it from the atmosphere. Microbes thrive when water and hydrocarbon fuel are together. Filter blocking is also caused by sterol glucosides, or SGs, found in vegetable oils. Without going into complex chemistry, SGs become fine solids dispersed in biodiesel. As ratios grew from B2 and B5 to B10 and even B20, the amount of filter clogging solids increased.

Fuel additives that control water are still the first line of defense against filter clogging. They slow slime growth. Not much can be done about SGs until refiners change blends from soy (which has 2,300 ppm SG) to corn (500 ppm) and sunflower (300 ppm) oils, but organic slime is still the main cause of filter plugging. LL